For many years, we were told that if we wanted to properly build our base fitness, we needed to spend 12 to 16 weeks riding long, steady, low-intensity miles to strengthen our aerobic systems, so they could eventually handle harder training rides and races. Well, this method works great if it’s your job to get up and ride your bike four to six hours a day, but for the rest of us without many free hours, a schedule-friendly method called polarized training presents a practical way to build endurance on a time budget. (For more tips on building endurance and speed quickly, check out Get Fast!)
As the name implies, polarized training emphasizes the opposite ends of the training spectrum, so in any given week you do both really hard efforts and easy aerobic rides: the best of both worlds. It’s a bit controversial (polarizing?) in a sports science community used to half-day base slogs, but it’s backed by a body of sound research.
“Ultimately, your ‘base’ comes down to your mitochondrial capacity,” says exercise physiologist Paul Laursen, PhD, of the training service lab PlewsandProf.com.
“Research shows that while longer, lower-intensity exercise increases the number of mitochondria in your cells, high-intensity training makes those mitochondria more powerful.” (Some studies show high-intensity exercise performed regularly can stimulate the production of mitochondria, too.)
Plus, when you do a set (or especially multiple sets) of high-intensity intervals, your heart rate stays elevated during your “recovery” periods, which benefits your aerobic energy systems—especially as the session progresses, says Laursen.
However you slice it, interval training undoubtedly improves endurance, even if you’re already pretty fit. “Our research has found that when well-trained cyclists performed two interval sessions a week for three to six weeks, their VO2 max, peak aerobic-power output and endurance performance improved by two to four percent,” he says.
To that end, the best recipe for building endurance is blending the distribution of your training so about 80 percent of your rides are in those aerobic ‘zone 2’ intensities (in terms of heart-rate zones) and about 20 percent are performed at high and very-high intensities, or a blend of zones 3 to 5 throughout the week, says Laursen. The Ultimate Endurance Interval
Cyclists looking to optimize their interval training for endurance benefits should perform intervals ranging between 30 seconds to 5 minutes, at a very hard intensity. These build your aerobic system while also being hard enough to recruit some fast-twitch sprint fibers, which makes those power-producing fibers more resistant to fatigue over time.
“Performing three to six of these leg-burning efforts, allowing one to two minutes of recovery in between, can have impressive effects,” says Laursen. As you gain fitness, increase the number of reps and the intensity.
Aim to perform these sessions twice a week, allowing at least a day of recovery in between. Then do the rest of the week’s riding at a moderate aerobic pace. Keep in mind, too, that if you’re planning to do a 100-mile ride, you still need to clock some longer days in the saddle so you can be comfortable on the bike, practice pacing, and dial in your nutrition and hydration—all things that shorter interval workouts can’t do.
Finally, remember that interval training, though beneficial, is also stressful. It’s essential that you not only include easy days and rest days in your weekly training plan, but also that you eat a balanced diet, get adequate sleep, and be mindful of your general recovery.
If you don’t, “you can end up fit but unhealthy with high levels of stress hormones and inflammation that can do real damage over time,” Laursen says. “It’s all about balance.”